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Changes in the Ozone Layer

This ThinkTV segment describes how the ozone layer is formed in the upper atmosphere, and how it serves to protect organisms from harmful ultraviolet rays. Depletion of the ozone, a process which began in the 1970s, was caused by CFCs. Today, the holes in the ozone layer appear to be shrinking.

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Scientists know that ozone can be both bad and good for us. Ozone is a pollutant in the lower atmosphere, or troposphere, the atmospheric layer nearest the ground. However, in the stratosphere, approximately 6 to 11 miles above Earth’s surface, ozone plays a critical role, protecting us from the Sun’s harmful ultraviolet radiation.

The "ozone layer," located in the stratosphere, contains 90% of Earth’s ozone and is beneficial to us because it absorbs ultraviolet (UV) radiation from the Sun. Ultraviolet rays can damage living things and increase rates of skin cancer and cataracts in humans. By blocking most of the ultraviolet radiation before it reaches the Earth's surface, the stratospheric ozone layer is critical to our survival.

British Antarctic Survey researchers first noticed the loss of ozone in the stratosphere during the 1970s.

Chemicals produced by humans, including chlorofluorocarbons (CFCs) once used in refrigeration and as propellants in spray cans, have damaged the ozone layer by releasing chlorine and bromine into the atmosphere. These chemicals prevent the formation of ozone, which creates “ozone holes." A diminished ozone layer allows more UV rays to reach Earth’s surface.

Scientists continue to study the ozone layer and ozone holes using satellite and ground-based data. To protect the ozone layer, many countries including the U.S. have signed an international treaty, The Montreal Protocol on Substances that Deplete the Ozone Layer, to reduce the amount of CFCs in the atmosphere. While the ozone hole over Antarctica continues to open and close, the ozone layer around the rest of the planet seems to be mending. Emissions of ozone-depleting substances are falling and predictions are that the ozone layer will recover by 2050. Even though the ozone hole and global warming are different problems, the ozone hole recovery may be affected by increases in the primary greenhouse gases, such as CO2.

Here are suggested ways to engage students with this video and with activities related to this topic.

Beginning a lesson: Provide each student with a blank map of the structure of the atmosphere. Have students label the various divisions and write down what they know about each layer. You can refer to Vertical Structure of the Atmosphere.

Viewing the video: Use the following suggestions to guide students’ viewing of the video.

Before: What are CFCs and where do they come from?

During: Is ozone always "good" or "bad?" Does ozone have the same impact on climate and health at all elevations?

After: How did human intervention correct a human-made problem?

Connecting to social studies: Have student groups examine the process by which international treaties are created, such as The Montreal Protocol on Substances that Deplete the Ozone Layer, and determine what governing body or bodies would enforce such a treaty. Why hasn’t a similar treaty been developed to reduce the amount of CO2 pollution on a global scale?